The Universal Serial Bus (USB) provides a cable bus that supports data exchange between a host computer and a large number and type of simultaneously accessible peripherals. For details, the reader is referred to the Universal Serial Bus Specification Revision 2 dated Apr. 27, 2000, available at www.usb.org.
Since the introduction and widespread adoption of the USB standard, a flood of USB peripherals has become available on the market. This matches the now-standard inclusion of one or more USB ports on most computers. USB peripherals have the desirable characteristic that they are hot-pluggable and generally require no installation and/or configuration of peripheral-specific drivers on the host computer.
In use, a USB peripheral is simply plugged into a host computer. Assuming that the Operating System (OS) has USB support, the peripheral is recognized and the USB bus is configured appropriately.
Almost all the standard peripherals have been made available as USB devices including storage devices such as standalone disk drives and ZIP or tape units.
The development of the USB has thus greatly simplified the addition of large numbers of peripherals in a highly flexible manner. It has also facilitated the expansion of systems, the size of which would have normally been constrained by the number of free PCI or ISA slots on an internal bus or devices configurable on a SCSI or IDE bus.
With the addition of a USB hub device, a standard external USB connection can be used to connect a larger number of USB devices. From the users perspective, this expansion capability is a vast improvement over the previous need to incrementally add peripherals as this process usually requires individual configuration, installation of drivers and often resolution of problems with IRQ conflicts and the like.
However, notwithstanding the use of SCSI buses and IDE expansion cards, internal device expansion capability remains problematic. The casual user is often faced with the need to reconfigure SCSI or IDE buses when adding extra disk storage. This process can involve relatively complex procedures sometimes beyond the capability of an infrequent user. Further, in some cases, expansion of internal components may be limited by inherent limitations in the hardware or system BIOS.
It would therefore be a significant advantage if internal USB components such as disk drives, CD/DVD/CDWR drives and the like could be easily installed and used with no or little reconfiguration of the system.
One solution is shown in FIG. 3 where an external backplate USB socket 17 is connected to an internal USB device 20 via a cable 30. This is generally a less suitable technique as it involves passing cabling through the chassis wall with attendant EMI and ESD problems. It is also unsatisfactory as an external cable may be prone to accidental disconnection.
Another interim development that is also suitable for legacy systems with no on-board USB controller is to use a USB PCI expansion card which is plugged into the PCI bus. An example of this is shown in FIG. 4 in a system having a USB hub on the motherboard. Such boards have the standard add-in card form-factor and, when mounted in a PCI socket, provide one or more USB sockets on the backplate of the PC chassis. Some USB expanders also provide an internal USB connection as shown in FIG. 4.
This solution may be satisfactory in some circumstances, particularly where USB devices are to be used with legacy equipment with no motherboard USB controller. However, as well as involving added cost, this technique consumes a PCI slot and in configurations where PCI slots are needed for other PCI interface cards for other peripherals this can be a problem. Also, using a PCI USB expander requires that the systems BIOS be capable of automatically configuring or at least recognizing the PCI device and/or that the PCI bus is hot-pluggable. Further, where an internal device is connected an external USB card port, the presence of a loose cable running from the exterior of the chassis to the interior may be undesirable as it requires an aperture in the chassis case which is not incorporated in a standard chassis and creates EMI and ESD weaknesses in the system. Also, this solution is generally not feasible for volume production.
The aim of the present invention is to provide an inexpensive and easily installed means for connecting internal USB devices to the USB without requiring PCI or ISA bus expansion boards and is compatible with standard motherboard configurations.